Though the wall vent removal

I have removed an old though the wall space heater….which went though a brick wall it is an 8 inch Vent.....for air intake and inside of the 8 is 4 inch for the flue. What I need is the plate ......A Terminal boot for the out side. ..Please advise me a what this part is truly called where to buy it......i will plaster the inside....however i need the plate for the outside